The actor's victory was controversial as he was sued in 2010 for sexual harassment and verbal abuse by two female collegues on the set of I'm Still Here. They later settled out of court, and Affleck has denied any wrongdoing.

Lonergan, who also won an Oscar for the movie, has defended the star in an op-ed for his alma matter Wesleyan University's student paper Wesleyan Argus, responding to an earlier piece by the paper's assistant opinion editor that accused the writer-director of complicity in Affleck's alleged actions.

"[Writer] Connor Aberle's article about myself, Casey, Affleck and Wesleyan's supposed complicity in condoning sexual misconduct - and worse - by tauting me as a Wesleyan alumn after I won an Oscar last week is such a tangle of illogic, misinformation and flat-out slander that only the author's presumed youth can possibly excuse his deeply offensive display of ignorance, and warped PC-fueled sense of indignation," Lonergan wrote.

Lonergan accused the writer of setting out his piece "as if Casey Affleck were actually guilty of a crime".

"It was alleged 7 years ago, in a civil lawsuit for breach of contract, that Casey sexually harrased two women formerly in his employ," he continued.

"Casey denounced the allegations as being totally fabricated. Like most civil suits, this one was settled out of court by mutual consent on undisclosed terms. In other words nothing was proved or disproved.

"So how does Mr Aberle dare to write as if he knows who was telling the truth and who was not? Anyone can sue anyone for anything in this country; the unsubstantiated details go in the public record and stay there.

"Somebody as interested in actual as opposed to merely vocalized social justice as Mr Aberle presumably is, should unwind his tangled, immoral chain of reasoning and start over at the fundamental precept that an allegation is not an indictment.

"Nor can it be treated as such by any ethical person living in a democratic society supposedly based on the rule of law."

Casey Affleck himself addressed the allegations in an interview following his Best Actor win, saying: "I believe that any kind of mistreatment of anyone for any reason is unacceptable and abhorrent, and everyone deserves to be treated with respect in the workplace and anywhere else.

"There's really nothing I can do about it. Other than live my life the way I know [how to] live it and to speak to what my own values are and how I try to live by them all the time."